Method for coating iron or zinc with phosphate composition and aqueous solution therefor



2,8 13,8 12 Patented Nov. 1 9, 1 957 METHOD FOR COATING IRON OR ZINC WITH PHOSPHATE COMPOSITION AND AQUEOUS SOLUTION THEREFOR Richard I. Somers, Northville, and John Rotsko, Detroit,

Mich., assignors to Parker Rust Proof Company, Dctroit, Mich., a corporation of Michigan No Drawing. Application June 24, 1952, Serial No. 295,336

Claims. (Cl. 148-615) This invention relates to improved solutions for and a method of coating surfaces of iron or zinc and has for its principal object the provision of a method of forming an improved phosphate coating which is especially suitable for receiving and retaining a final finish of organic protective material such as paint, lacquer, varnish, etc. An equally important object is to provide materials suitable for use in forming such coatings on surfaces of iron, zinc and their alloys.

The formation of phosphate coatings on surfaces of zinc and its alloys from phosphoric acid solutions containing a nitrate accelerator, is disclosed in U. S. Patent No. 1,221,046. More uniform phosphate coatings are allegedly formed from the solutions of U. S. Patent No. 1,221,046 when nickel or cobalt ions are added thereto, and this improvement is taught in U. S. Patent No. 2,121,574. U. S. Patents 1,869,121 and 1,888,189 disclose the fact that the copper ion in certain concentrations is beneficial in speeding up the action of a phosphate solution on a Zinc surface. Zinc surfaces containing small proportions of aluminum are coated only with great difficulty with the above nickel ion accelerated solutions, but may be easily coated with solutions altered by the presence of small quantities of fiuoborate ion in combination with nickel ions as is disclosed in U. S. Patent No. 2,591,479. In times of emergency and of strategic material shortages, it is often difficult to obtain nickel in sufficient quantity to satisfy even the more critical needs, and a material which is plentiful and inexpensive is highly desirable as a replacement therefor.

The present invention is concerned with materials and solutions of the general type hitherto known and a method of applying such solutions to surfaces of iron or zinc and their alloys, which solutions are improved, however, in the respects that the materials utilized are more uni formly available and less expensive than hitherto used materials and the resultant coatings are harder, more adherent, less subject to flaking and in general, better adapted to receive a siccative coating such as paint or the like. Furthermore, control of the solutions in operation is rendered less difiicult than that characteristic of hitherto known operating solutions. As used in this specification and in the appended claims, the term zinc surface" is intended in a broad sense to include any surface which is predominantly zinc, such as electrogalvanized ferrous surfaces, zinc hot dipped ferrous surfaces, zinc die castings, surfaces coated with zinc alloys, etc.

The present materials and solutions differ from previously known and used phosphate solutions in that they employ copper and nickel ions in combination in certain critically restricted ranges. As suggested above, copper ions have been used in phosphate coating solutions as the sole metal ion and in the same manner the nickel ion has also been employed. The new and improved results of this invention are based upon the discovery that certain concentrations of the combination of nickel ions and copper ions unexpectedly produce coatings which are lilLl-J tit-use, adherent and which have greater resistance to corrosion than coatings formed from identical solutions except containing only nickel ions or only copper ions.

The phosphate coating solutions which are improved by the addition of the specific combinations of nickel and copper ions of this invention, are fundamentally conventional solutions and for the purposes of this invention may contain as essential ingredients about .5 to 2.5% P04 ion, sufiicient zinc or manganese ion to form dihydrogen phosphate with the phosphate ion, and an amount of an oxidizing ion such as the nitrate or nitrite ion or a mixture of nitrate and nitrite ions. The quantity of nitrate ion which is desirable is about 0.2% to about 1% with the major beneficial effects being obtained at about 0.3% N03. Where nitrite is used, substantially smaller quantities are required to produce acceleration and 0.002% to 0.008% NOz may be satisfactorily employed. The optimum concentration of nitrite is about .004%.

The above solution are converted into the improved solutions of this invention by adding proportions of the nickel ion between about 0.0l% and 0.4% and the copper ion between about 0.0003% and 0.005%. The major beneficial effects of the addition are gained when the concentration of nickel ion is about 0.02% to 0.05% and the copper concentration is in the range of about 0.002% to 0.003%. Inasmuch as one of the purposes of the invention is to replace nickel, the latter range of concentrations of nickel and copper ions is preferred. In the presence of at least .0l% nickel, concentrations of copper in the solutions above about 0.005% have been found to form a coating having a reddish appearance and less desirable characteristics as a base for paint including less resistance to corrosion and less paint adherence. Proportions of copper below about .0003% apparently do not coact with the nickel in such a way as to appreciably reduce the amount of nickel which is required, whereas with quantities of copper ion above about .0003%, a threshold is passed at which the amount of nickel required drops from a preferred concentration of about .3% to a value between about 02% and .0593. Due to the fact that copper is depleted slowly as work is processed through the bath, it is desirable to maintain an excess over and above the minimum or threshold value with 0.002% to 0.003% being preferred.

The nickel and copper ions may be introduced into the solution in the form of a salt which is soluble in the solution, for example, as a carbonate, nitrate, chloride or sulfate and preferably as the carbonate.

Aqueous phosphate solutions containing nitrate or nitrite and the combination of copper and nickel ions in the ranges of concentrations given above, form hard, ad herent coatings on iron and zinc surfaces as well as zinc treated iron surfaces commercially known as hot dip zinc, electrogalvanized metal, annealed galvanized metal. etc. In the commercial processing of iron having various zinc surface treatments or in mixed processing in which some articles are all iron, some all zinc and some galvanized, etc., it is most advantageous to employ nitrite as the accelerator, or to use an admixture of nitrite and nitrate. The presence of nitrite in the treating solution tends to enable the use of lower temperatures, to precipitate ferrous iron as an insoluble iron phosphate thereby keeping the solution substantially free of ferrous iron and to thereby promote the formation of a desirable coating on the iron surfaces as well as the zinc surfaces. When using combinations of nitrite and nitrate, the above given ranges of concentration of nitrite or nitrate for use separately may be employed.

Predominantly zinc surfaces which contain alloying constituents such as aluminum in sufficient quantity to render phosphate solutions containing nickel and nitrate or nitrite ineffective in forming a coating thereon, may be coated if the solutions are altered to contain in addition a small quantity of the fiuoborate ion. Satisfactory coatings are formed from solutions containing about 1% to 2% phosphate ion when the nickel ion concentration is at least 1% and the fiuoborate concentration is at least .1692. For best results the nickel ion concentration should be about 3% and the fiuoborate ion about 24%. in such solutions, the use of the copper ion in combination with the nickel ion reduces the quantity of nickel ion which is required. For example, in the pres ence of 002% to 003% copper ion in a solution containing 14% fluoborate and 1% phosphate (as zinc dihydrogen phosphate) and 0.3% nitrate, excellent coatings arc obtained on zinc surfaces containing some aluminum when the nickel concentration is between about 0.1% and 0.15%. While more nickel up to about .3 or 0.4% does not detrimentally affect the quality of the coating, quantities above about 0.15% are unnecessary for good results. The presence of the fiuoborate ion is not detrimental to the formation of coatings on the more easily coated metals, and therefore, a composition having a wide range of usefulness on surfaces of iron, zinc or their alloys is given in Formula I.

Sufficient to form rilhydrogou pho phate with P; To make solution Solutions of the above types may be applied to the surfaces to be coated either by immersing the article in the solution or spraying or flowing the solution over the surface. The conditions for application are not critical and may be varied considerably in accordance with practices which are now well known in the art. Examples of typically suitable operating conditions are given in the below examples which illustrate the invention in greater detail.

Example I A coating solution was built up containing the following ingredients:

Grams/ liter Phosphoric acid, HaPO4 (75%) 7.8 Nitric acid, HNOs (32 B.) 2.3 Zinc oxide, ZnO 2.4 Copper carbonate, CuCOa .03 Nickel carbonate, NiCOa .39

This solution containing about .0015% copper ion and about 02% nickel ion was placed in a suitable container and the temperature raised to about 130 F.-180 F. A plurality of electrogalvanized steel panels were immersed in the solution for about one minute and an especially adherent. hard and dense coating having high resistuicc to dislodgment was formed on each panel. Coating weights were found to vary between about 250 and 350 tug/sq. ft. On subsequent painting, excellent adhere cc ot the paint was obtained, and high resistance to corrosion from salt spray and humidity were observed.

Additional hot-dip zinc and iron panels were processed and comparable coatings in appearance, Weight and corrosion resistance as a base for paint were obtained.

lron, hot-dip zinc, electrogalvanized and aluminum containing zinc treated panels were immersed in the solution for thirty seconds to one minute at F. to 180 F. Coatings comparable to those of Example I were obtairted.

Example III A concentrate was made up containing:

Grams HsPOi (75%) 24 HNO3 (32 B.) 7.3 ZnO 7.2

Water to make 5-4 grams.

A plurality of processing solutions were formed by using 18 grams of the above concentrate and making up one liter volume and adding varying proportions of copper carbonate to form copper ion concentrations of 0.0003%, 0.0015%, 0.0025%, .0035%, 004%, 005%, 006% and 008%. Another series of processing solutions was formed by adding to 18 grams of the concentrate in one liter, proportions of nickel carbonate to provide nickel ion concentrations of 0.001%, 0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.3%, 0.5%.

Electrogalvanized steel panels were immersed in each solution at F.-l50 F. for about 15 seconds. The copper ion containing series of solutions produced heavy, soft coatings having a dark gray color with the weight of the coatings generally increasing with increasing copper concentration. The nickel ion containing series of solu tions produced coatings at concentrations above 02% which were soft and heavy with the color being somewhat lighter than the copper ion accelerated coatings. Very little coating was formed at concentrations of nickel below about 02% and of copper below about 006%. Of the coatings which were formed, the nickel ion accelerated coatings were somewhat better than the copper ion accelerated coatings as a base for paint, but both types of coatings were undesirably soft.

A third series of solutions was formed from the above concentrate by using 18 grams of concentrate per liter and adding nickel and copper carbonate to form copper and nickel ion concentrations of:

Percent Percent Copper Nickel 1011 Ion Electrogalvanized steel panels were sprayed with each of the solutions 1 to 10 for two to fifteen seconds at about F. Dense, adherent, hard coatings having coating weights varying between about 100 to 250 milligrams per square foot were obtained from solutions 1, 2, 3, 4. 6, 7 and 10. Solutions 5 and 8 formed more fiocculent, softer and heavier coatings of the type obtained in the presence of only copper ions or nickel ions in the solution. The coatings obtained from solutions 6 and 7 were comparable to those obtained from solutions 1, 2, 3, 4 and i0 and no advantage appeared to be gained by having nickel present in quantities above 0.05%. Coatings produced from solution 9 were heavier and more flocculent than those from solutions 1, 2, 3, 6, 7 and 10 and had a reddish copper color.

Inasmuch as the ingredients in the processing solutions are depleted during use, it is necessary to periodically replenish the processing solutions to maintain proper balance in the solution. For solutions containing no fluoborate ion, a suitable replenishing solution is as follows:

Grarns H3PO4 (75%) 260.0 HNO3 (32 B.) 77.00 ZnO 82.0

CuCOs 1.0

NiCOs 5.0

Sufficient water to dissolve.

For solutions containing fiuoborate, a suitable replenishing solution is:

Grams HsPOs (75%) 260 HNOs (32 B.) 77.00 ZnO 82.0

CuCOs 1.0 NiCOa 5.0

NaBF4 80 What is claimed is:

1. An aqueous solution for coating iron or zinc surfaces, said solution comprising as the essential coatingproducing ingredients about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.01 to 0.4% nickel ion, 0.0003% to 0.005% copper ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrate ion in a concentration of about 0.2%1% nitrate ion and 0.002% to 0.008% nitrite ion.

2. An aqueous solution for coating iron or zinc surfaces, said solution consisting essentially of about .5 to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.02% to 0.05% nickel ion, 0.002% to 0.003% copper ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a concentration of about 0.2%-1% nitrate ion and 0.002% to 0.008% nitrite ion.

3. An aqueous solution for coating iron or zinc surfaces, said solution consisting essentially of about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.01% to 0.4% nickel ion, 0.0003% to 0.005% copper ion, 0.16% to 0.4% fluoborate ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrate ion in a concentration of about 0.2%-1% nitrate ion and 0.002% to 0.008% nitrate ion.

4. An aqueous solution for coating iron or zinc surfaces, said solution consisting essentially of about .5 to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.02% to 0.05% nickel ion, 0.002% to 0.003% copper ion, 0.16% to 0.4% flnoborate ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a concentration of about 0.2%1% nitrate ion and 0.002% to 0.008% nitrite ion.

5. The method for coating iron or zinc surfaces which comprises the step of contacting the surface with a solution consisting essentially of about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.01% to 0.4% nickel ion, 0.0003% to 0.005% copper ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a concentration of about 0.2%1% nitrate ion and 0.002% to 0.008% nitrite ion.

6. The method for coating iron or zinc surfaces which comprises the step of contacting the surface with a solution consisting essentially of about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.02% to 0.05% nickel ion, 0.002% to 0.003% copper ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a con centration of about 0.2%l% nitrate ion and 0.002% to 0.008% nitrite ion.

7. The method for coating iron or zinc surfaces which comprises the step of contacting the surface with a solution consisting essentially of about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.01% to 0.4% nickel ion, 0.0003% to 0.005% copper ion, 0.16% to 0.4% fiuoborate ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a concentration of about 0.2%1% nitrate ion and 0.002% to 0.008% nitrite ion.

8. The method for coating iron or zinc surfaces which comprises the step of contacting the surface with a solution consisting essentially of about .5% to 2.5% phosphate ion, an ion of the group consisting of the zinc ion and the manganese ion in a proportion to form dihydrogen phosphate with said phosphate ion, 0.02% to 0.05% nickel ion, 0.002% to 0.003% copper ion, 0.16% to 0.4% fluoborate ion, and at least one oxidizing ion selected from the group consisting of the nitrate ion and the nitrite ion in a concentration of about 0.2%1% nitrate ion and 0.002% to 0.008% nitrite ion.

9. A solution for replenishing the phosphate coating solution of claim 1, said replenishing comprising as essential ingredients, 260 grams HaPOa, 77 grams HNOa (32 B.), 82 grams ZnO, 1 gram CuCOs, 5 grams NiCO3, H2O suificient to form a solution.

10. A solution for replenishing the phosphate coating solution of claim 3, said replenishing solution comprising as essential ingredients, 260 grams 75 H3PO4, 77 grams HNO3 (32 B.), 82 grams ZnO, 1 gram CuCOa, 5 grams NiCOa, H2O snfiicient to form a solution, and 80 grams NaBF4.

References Cited in the file of this patent UNITED STATES PATENTS 1,949,090 Tanner Feb. 17, 1934 2,164,042 Rornig June 27, 1939 2,500,915 Tanner Mar. 14, 1950 2,554,139 Drysdale et a1 May 22, 1951 2,591,479 Ward Apr. 1, 1952 FOREIGN PATENTS 126,733 Australia Feb. 6, 1948 805,845 France Sept. 7, 1936 

1. AN AQUEOUS SOLUTION FOR COATING IRON OR ZINC SURFACES, SAID SOLUTION COMPRISING AS THE ESSENTIAL COATINGPRODUCING INGREDIENTS ABOUT 5% TO 2.5% PHOSPHATE ION, AN ION OF THE GROUP CONSISTING OF THE ZINC ION AND THE MANGANESE ION IN A PROPORTION TO FORM DIHYDROGEN PHOSPHATE WITH SAID PHOSPHATE ION, 0.01% TO 0.4% NICKEL ION, 0.0003% TO 0.005% COPPER ION, AND AT LEAST ONE OXIDIZING ION SELECTED FROM THE GROUP CONSISTING OF THE NITRATE ION AND NITRATE ION IN A CONCENTRATION OF ABOUT 0.2%-1% NITRATE ION AND 0.002% TO 0.008% NITRITE ION. 